C-SAM is a non-destructive alternative that a lot laboratories and chip manufacturers use. Dye and Pry would work I suppose although I have never done it in practice with PoP but it should be any different for PoP.

Dye and pry is frequently used on BGAs to determine if there is a crack at the board level or component level interconnect. C-SAM will show internal delaminations of components, not sure how well it would work with solder joint cracks. You can also do cross-sections to look at each solder joint.

In my opinion destructive methods went out with the stone age. At least they did at our company. We specialize in non-destructive defect analysis. We can determine where the failure is i.e. assembly process, fab defect, BGA defect or plating process. After documenting the defect we will take corrective action to resolve the issue and provide you with working product to confirm our prognosis. Contact me if you will like to discuss in detail